1. Field of the Invention
The present invention relates to an optical recording apparatus which uses an optical head for emitting a main beam and a sub-beam succeeding the main beam formed by diffraction of an optical beam from a light source, in order to read, from the sub-beam, a recording signal which has been recorded by the main beam on an information recording medium.
2. Description of Related Art
CD-R/RW drives for CD-R (Recordable) and CD-RW (ReWritable) systems of the CD family are well known optical disk recording apparatuses for recording a digital data signal onto a disk using an optical beam emitted from an optical head. Efforts are being made to increase the recording speed of such optical disk recording apparatuses.
Disks for use in recording by such optical disk recording apparatuses may have different recording sensitivities, depending on materials or manufacturer. Even disks manufactured by the same manufacture may differ in recording sensitivity due to manufacturing variation. Even in a single disk, different sections may have different sensitivities.
In optical disk recording apparatuses, it is therefore necessary to control an emission power of the optical head when recording so as to compensate for variations in recording sensitivity among disks, to thereby set the emission power of the optical head at an optimum level for disk recording.
For recording on CD-R disks, for which the recording speed has been increased to a high speed which is about 25 times faster than the normal speed, the recording conditions must be set strictly. This produces a necessity of so-called running OPC (Optimum Power Control) for controlling an emission power of the optical head by detecting the recording state of a recording signal recorded on the disk, in the disk recording operation.
Although detection of the recording state of the recording signal recorded on the disk is required so as to perform running OPC, it is difficult to detect the recording state of an actual recording signal during the recording operation. Accordingly, a method of detecting the recording state by detecting a reflection level of a recording pulse which is used for recording a recording signal has been implemented. With this method, however, the emission power of the optical head is not always set at a true optimum recording level because the recording state of the data recorded in the disk is not actually detected.
In order to overcome the above problem, a technology in which a sub-beam succeeding the main beam is further formed from an optical beam emitted to the disk from the optical head along with the main beam used for actual recording, and the recording signal recorded by the main beam is read using the sub-beam to thereby detect the recording state can be considered.
In optical disk recording apparatuses, a Differential Push-pull method is generally used for tracking control such that the 0th order beam of a diffraction beam from the optical head is used for the main beam and the ±1st order beams are used for the preceding and succeeding sub-beams for tracking control. However, this method has a problem that because in a state in which a tracking control signal is obtained optimally, namely in a state in which the main spot formed by the main beam is correctly located on the signal track, each sub-spot formed by each sub-beam is set at substantially the middle of adjacent signal tracks, a recording signal cannot be read in a good condition even when the succeeding sub-beam is used.
Further, although use of the succeeding sub-beam, of the ±2nd order beams of the diffraction light from the optical head, can be considered, S/N of the recording signal which is read is not preferable because the light amount of the ±2nd order beams of the diffraction light from the optical head is significantly less than that of the ±1st order beams.